Remote control system



Feb. 6, 1945. P. B. HExNEcK E'rAl. O 2,358,659

REMOTE CONTROL SYSTEM Filed Deo. 28, 1942 Patented Feb. 6, 1945 OFFICE REMOTE CONTROL -SYSTEM Paul Benjamin Helneck and Alvin A. 'Meddocln North Hollywood. Calif., assignors, by mesne as-V signments, to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application December 28, 1642, Serial No.470,35 l

l (ci. so-54.5)

7 Claims.

This invention relates to fluid pressure systems for controlling elements remotely locatedV from the operator, and relates more particularly to a fluid pressure control system capable ofl fulfilling the exacting demands of military airplanes.

Although this invention will be described as applied to the demands for airplane control, it is applicable to other uses. Airplaneshave many units which must be accurately controlled and continuously moved during flight for maximum performance. These units may be quite remote from the pilot or engineer; such as engine controls on a multi-enginedvbomber or transport. For example, engine throttle, carburetor heat, oil

coolers, cowl flaps, etc., must be carefully controlled at all times. This requires controls from the operator to the unit which controlsare infallible in operation and exact in synchronization so that movement of the control will cause a movement of the controlled unit which is exactly the same.

In the past; cables have been largely used for this purpose, and have been formed in the necessarily tortuous path by the use of pulleys mounted on structural members within the wing. In other instances push-pull cable and housing units have been used. In either case, these mechanical controls are unsuited for the largest of modern planes because of the large amount of friction in long systems. is to provide airplanes with hydraulic (or pneumatic) control systems wherein there is little appreciable increase in friction with increased lengths of control systems.

The requirements of airplane controls are exacting. The driven unit must move exactly the same amount as the operators control. Thus there can be no free play, lost motion or back lash in thr` hydraulic system. Further, the operators control must be synchronized with the resultant movement; that is, r4the end of the operators stroke must also be the end of the stroke of the driven unit. Thermal expansion of iiuid must be provided for so that conduitswill not be burst.v v

vbe provided to lock the systembetween operations so that extreme vibration or changes in load will not upset the setting. Further, in military airplanes, provision must be made so The trend, therefore,v

that the control system will belentirely cutout if part of it is shot away or damaged, permitting the throttle, etc., to return to a given position unit 22 also.

for steady operation. AThe present inventionis a two line, master cylinder and motor cylinder system having as parts thereof the necessary construction to provide these desirable functions.

It is, therefore, an object of the invention to provide a fluid control system eliminating the effects of uid expansion .and contraction.

. Another object is to provide a, fluid pressure system which is initially biased or pressure loaded to remove all slack and back lash.

Still another object is to provide a fluid pressure systemwherein the master and motor unitsv are automatically indexed so as to provide synchronism of subsequent movement of the units.

VA further object is to providea fluid system having a hydraulic lock so that differences of loading or vibration will not aect the position setting of the system.

Another Objectis to provide means combined with the hydraulic lock to release the lock upon a break in any conduit of the system, permittingv the'motor cylinder to return to aA predetermined spring biased position.

Still another object is to provide means -to close off the preload of the system whenever the conduits are broken by gu fire.

Other objects and advantages of the systems will become apparent in the following description and claims. l

The drawing forming a part of this specication isa, schematic drawing in full section, of the entire system and the parts thereof.

Referring to 'the drawing, power is generated in a master cylinderunit l0 including a cylinder housing l2, and a piston Il therein connected to apiston rod I6. Pivoted to cylinder I2 is a link I8, to which is pivoted a manual handle 20, pivoted also to piston rod I6. The control unit shown is manually operated, but it will be appreciated that 1t could also be power driven insofar as the function of the system is concerned.

Leading from the left end of master cylinder III 'and connected to a motor unit 22, is a conduit 2l. A similar conduit 26 is connected to theright end of master cylinder'l, and'leads to motor Motor unit 22 includes a cylindrical portion 28, in which is placed a reciprocal piston 30,'having a piston rod 32. ',listonv 30 has a y hole 3l therethrough, in which are placed valve poppets 36 and 38, oppositely biased by a common I spring 40. Poppets 36 and 38 are the means by Y 44, which hold' piston 36 in a. predetermined position when no other forces are applied to it. For example, if pistonrod 32 is connected to the throttle of an airplane motor, springs 44 and 42 will hold the throttle in a position about 60 percentopen.

Conduits 24 and 26 connect with an auxiliary cylinder 46 in slave housing 22, in which cylinder there is placed a pressure-'responsive shuttle piston 48 normally centered by two springs 56 and 52 respectively. Springs 56 and 52 are not strictly struction is provided on the right end of cylinder 46. Therea chamber 62 has an opening to chamber 46, which is normally closed by a poppet 64,. urged toward its seat by a conical spring 66. A passage 68.connects chamber 62 with the right end of motor cylinder 28.

The structure just dei'lned comprises a' hydraulic lock for the motor cylinder 28. Thus, when motor cylinder 28 is lled with uid, piston 36 is prevented from moving in either direction by poppets 56 and 64, which seal the flow of fluid which might otherwise occur if a load were placed upon piston rod 32. When it is desired to operate the motor piston 36 in one direction or the other, pressure is appliedv thereto by moving manual handle 26 on the master unit in the desired direction. The fluid pressure thus generated opens either poppet 64 or 56 so that su to the extreme right, poppet sa win not be opened. This means merely that there is too muchfluid in the other half of the system which can be corrected by moving the master piston I4 in the opposite direction, to relieve the excess of i'luid from that half of the system, as has just been described.

The remaining elements of motor unit 22 comprise means to release the hydraulic lock just described in the event that either.v conduit 24 or conduit 26 is shot away, or otherwise broken during ight of an ainplane in which the system is placed.' Release of the hydraulic lock is necessary because breakage of the conduits make further control impossible, and the particular control device, for example the throttle, should be automaticallypositioned by springs 42 and 44 to a predetermined position, which,l in the case of a throttle, may be 60 percent open. Since a break in either conduit means a relief or release of' pressure in that conduit, means are provided to respond to such 'a drop in pressure to release poplpets 56 and 64, which form the hydraulic lock. Accordingly, in the left half of motor unit 22, a passage 16 is provided leading from conduit 24 to a chamber 12, in which is the i'luid pressure is applied to the adjacent end of the cylinder 28 through passage 68 or 66; the uid pressure also forces the shuttle piston 48 toward either poppet 56 or 64 to release it and permit uid to exhaust from the adjacent end of the cylinder 28. This action permits the motor piston 30 to move under the inuence of the generated pressure. When the handle '26 has been moved to the end of its travel and has been released, the motor rpiston backs up a few thousandths of an inch, permitting the piston 48 to restore and the exhaust poppet to close. Although, for purposes of clarity, a considerable @an is shown in the drawing between the stems of piston 48 and the poppets which the piston contacts, in actual practice this clearance is reduced to a few thousandths of an inch on each end; for example, four-thousandths of an inch.

The automatic indexing means in piston 36 'l :operate as follows tosynchronize movement of motor 'piston 36 with master piston I4: if master piston I4 is -moved to one extreme of its stroke gby manual handle 20, for example to the left,

,there may be too much fluid in the conduit and the motor unit 22, preventing master piston I4 from reaching the extremeend of master cylinv der I2. However, when motor piston'36 reaches the extre e end of its stroke, which will be the rright end f motor cylinder 28, the stem on poppet 38 willcontact the end of cylinder 28, opening passage 34 through piston 36. In this case, continued pressure upon master piston I4 has caused uid under pressure to lift poppet 36 off of its seat and flow through the piston 36 to the other en'd f piston 36. This action continues until master piston I4 reaches the extreme end n of its stroke, at Iwhich time fiow through piston 36 ceases. If too little .uid is present in conduit 24 and slave unit 22 to move slave piston placed a piston 14 resting on a shoulderand urged to the left by a spring 16. Piston 14 has a lost motion connection 11 with poppet 56, so that poppet 56 will be pulled oi of its seat when piston 14 moves to the left. The chamber retaining the spring 16 is vented to atmosphere by a rpassage 18, shown in dotted outline. Piston 14 is held on its shoulder, in the position shown, by a preload of three hundred pounds o the entire hydraulic system, which will be explained later. When conduit 24 isv shot away, this preload pressure will be relieved in the broken conduit 24, and spring 16 will urge piston 14 to the left, pulling poppet 56 off of its seat.

The stillness of spring 16 is insuiiicient to overcome the force exerted on piston 14 by the preload pressure but it is much stiffer than the spring 58 and the spring of poppet 86. 1n fact, the springs on poppets 86 and 84 and on poppets 56 and 64 are only stiff enough to seat the valves in the absence of any appreciable differential uid pressure working against them. Furthermore, the eil'ective areas of the poppets 86 and 84 and 56 and 64 may be relatively small so that the forces applied to those poppets by the fluid pressure are small as compared to the forces exerted by the springs 16 and 96.

When piston 14 moves to the left due to release of the preload when conduit 24 is broken, it not only pulls poppet 56 oi its seat to release the hydraulic lock on that side, but it also opens a poppet 86 which controls ow from a rpassage 82 to the outer side of a similar poppet 84 on the extreme right of motor unit' 22. This action of Opening poppet 86 vents passage 82 to atmosphere when the line is broken, relieving pressure behind poppet 84 also. This release of pressure lpermits the preload in the right side of motor unit 22 to lift poppet 84 off of its seat, venting the preload to atmospheric pressure. After a minute ow of preload uid, the preload is automatically cut olf as will be explained later, allowing the remaining fluid in conduit 26 and the right end of slave unit 22 to be vented to atmospheric pressure through poppet 84. This release of pressure permits a piston 86 in the right half of slave unit 22, corresponding to piston v14, to move to the right in its chamber 88 under the iniuence of a spring 86. .Piston 86 has a. lost the poppet off its Vseat releases the pressure in the closed space. Y

If conduit 26 is shotm away instead of conduit 24. this same sequence of events takes place, but in the reverse direction.

From the foregoing, it is quite evident thatY the operation of the fluid trap and the trap release mechanism are closely interrelated, and

further that the operation ofthe uid trap rellease is clearly facilitatedby the presence of a preload in the hydraulic system. The mechanism for providing the preload and the expansion relief will now be described.

` Placed between conduits 24 and 26 in the drawing is an accumulator supplying hydraulic :duid under a substantially constant pressure; for

example, two or three hundred pounds. Accumulator |00 is connected by a conduit, |02 to a T member |04, having a iluid conduit |06 leading to conduit 24 and asimilar conduit |08 leading to conduit 26. In the upper part of T member |04 is a `puppet ||0 seated in cylindrical chamber ||2- very closely, but urged away 'from its seat. by a coil spring ||4. The fit of A POPpet. |I0 il. its chamber `||2 is such that a few drops a minute may leak past the poppet H0 without causing movement of the same, but if a sudden ow from accumulator |00 should ne encountered, the diierence in pressure present would seat poppet ||0` against the force of its spring ||4 and stop all further flow from the accumulator. This action takes place when The invention has now been described completely in accordance with the patent statutes. Y

Although' this description haslbeen -mad'e with reference to a particular embodiment thereof, it isnot limited to these embodiments, nor otherf wise, except by the terms of the following claims.

Weclaim:

1. In a'hydraulic remote control system comprising a master unit and a motor unit interconnected by a gpair of iiuid conduits, the master unit including means for selectively circulating fluid through either conduit to the motor. unit and back from the motor unit through the other conduit to' the master unit, and the motor unit including cylinder means and piston means reciprocal therein in response to said uid circulation: means for normally maintaining a. pre- 'load pressure in both said conduits substantially in excess of the magnitude of the differential pressure between said tw'o conduits resulting from said fluid circulation produced by said master unit; and means in said motor unit responv sive to failure of said preload pressure for establishing direct nuid connection between opposite ends of said motor cylinder whereby the motor piston is released from hydraulic control.

2. A system as described in claim 1 in which said last mentioned means includes an auxiliary either conduit 24 or 26 is shot away, in which case there is a sudden release of pressure within T member |04, which seats poppet I0. Thus, whenever there is a break in a conduit there is little' uid lost from the accumulator. As contraction of hydraulic fluid occurs in either master cylinder, motor unit22, or conduit 24 or 26, as when an airplane ies tothe frigid altitudes,

.this deficiency in volume will'be made up by the slow flow of uid around poppet ||0 from accumulator |00. such a case the fluid merely lifts check poppets ||6 and |||ll off of their seats to reach connected conduits |08 and |06 respectively. Thus at all times the preload pressure is present and the hydraulic store of fluid in accumulator |00 supplies any deficiency of fluid due to contraction leakage. y

If expansion of the fluid -should be encountered, as when an airplane descends from a high altitude to aground station, at a high temperature, this expansion will cause an increase in pressure in the conduitslfabove the preload pressure and above the operating pressure for the system. In this event, relief valves 20 and |22 may be overcome, ventingthis surplus; volume to the accumulator |00 through passages |24 and |26, in T member |04. By accurately adjusting" relief valves |20 and |22 to relieve at the same high pressure, the volume of iuid re-` moved or relieved from the system will represent only that portion due to thermal expansion, and

not.` any due to actuation pressure generated by the master cylinder unit I0.

cylinder having one end connected to one of saidv conduits and the other end vented to atmosphere, an auxiliary piston in said auxiliary cylinder normally maintained in said other end thereof by preload pressure in said conduit, spring means for moving said auxiliary piston to said' one end of said auxiliary, cylinder in response to failure of said preload pressure, and valve means responsive, to movement of said auxiliary piston by said spring means for directlyl interconnecting said two conduits. y

3. rThe hydraulic remote control system as described in claim lv in which said last mentioned means includes a short,I circuiting passage, a check valve means at each end of said passage communicating with said uid conduits, each check vvalve permitting ow from the associated conduit into said short circuiting Apassage y but normally preventing reverse ow, a pair of auxiliary pistons, one associated with each o'f said check valves and arranged to open its associated check valve in one end position, the said one end of each auxiliary piston being permanently connected to its associated conduit whereby preload pressure in said conduits maintains said auxiliary pistons out of opening relation .with their associated check valves, and spring means associated with each auxiliary piston for moving it into position'to open its assocated' check valve in response to failure of pre1 pressure in the associated conduit.

4 A hydraulic remote control system as described in claim 1 including in said motor lunit.

a pair of checlr valves one between each of Asaid conduits and said working cylinder for normally permitting ow from the conduit into the motoi-cylinder while preventing reverse now, means responsive to differential-pressure between said two conduits for olpening. the check valve asso-- ciated with the conduit of lower pressure; said last mentioned means of claim 1 including.

means for directly interconnecting said two conduits at the motor unit and means for opening said check valves.

5. The hydraulic remote control system. as clescribed in claim 1in which said means for normally ymaintaining a preload pressure-comprises l ling al1 flow between said reservoir and said conduit in response to a pressure drop between said A reservoir and said conduit in excess of a prede'- termined value.

6. A hydraulic remote control system as described in claim 1 in which said means for normally maintaining a preload pressure comprises Va reservoir of fluid under preload lpressure, means dening a passage, "valve means for normally permitting slow o'w of fluid in either direction between said reservoir and said passage, means for preventing ow from said reservoir to said passage in response to a predetermined drop of to said conduits, and separate relief valve means for permitting a now of fluid from either conduit-to said passage in response .to a. predeterf mined rise in the pressure in the conduits above the pressure in said passage.

7. A hydraulic remote control system comprising a master unit and amotor unit interconnected by a pair of uid conduits, means Vfor normally maintaining a preload pressure in said system comprising a source of uid under pressure, means providing a restricted passage between said source and said system for permitting slow dow of fluid between said source and said system in. either direction to compensate for contraction and expansion of the uid in said system and means responsive to a substantial the pressure in said passage below the pressure in said reservoir, check valve means independently connecting said passage with each conduit for permitting free flow of uid from said passage pressure drop in said system relative to the pressure in said source for blocking all' fiow of fluid l from said source to said system.

PAUL BENJAMIN HEINECKQ ALVIN A. MEDDOCK. 

